The history of intraocular lenses (IOLs) is a long and varied one. Intraocular lenses can be used to treat a wide diversity of eye conditions ranging from cataracts to any type of eyesight correction. In addition, IOLs can be used to replace an irreversibly damaged lens in the eye—aphakic eyes. Alternatively, the lenses can be used in addition to the natural lens to correct the vision—phakic eyes. These lenses can be placed in the anterior or posterior chambers of the eye.
Early IOL researchers were plagued with problems associated with the materials which were obtainable to them at the time (early 1950's) making the lenses too heavy and too large. Surgery of the eye was in its infancy and therefore there were many problems with the surgical procedures. Since that time the quality, size and weight of the optics as well as microsurgical procedures have dramatically improved.
The earliest IOL's were placed in the anterior chamber of the eye, this being the easiest chamber to get to. Along with the early problems with the optics and surgical techniques, placement of a lens in the anterior chamber proved difficult because the anterior chamber is narrow (about 1.5 to 2.5 mm).
The second location is the angle between the cornea and the iris. Angle supported anterior chamber IOLs took advantage of the anterior chamber angle to support and fix the IOL in place. By angling the IOL into opposite sides of the anterior chamber, the natural angle was used to keep the IOL from moving. However, early lenses experienced marked problems with endothelial loss due to chafing against the early thick lenses. Later lenses were able to reduce the significance of this problem, but still retained problems associated with placement of the IOL in the chamber angle. The biological properties of that angle make it a very sensitive area. The structures associated with equalizing the internal pressure of the eye are located in that area. Additionally, the tissue in the area is easily irritated and irritation initiates a growth of fibrous tissue, called synechiae. The IOL fixation must be gentle in order to reduce irritation, but stable enough that it will not be easily moveable. This compromise is difficult to obtain. In addition, although the results were excellent in the short-term, there was a significant problem in the long term with altered night vision, loss of endothelial cell populations and alteration of the anterior uvea. These problems as well as the fact that such anteriorly positioned lenses were uncomfortable to the patient, caused many doctors to abandon anterior chamber IOL's.
A third location was developed later and involves implanting a contact lens between the iris and the natural lens. These lenses are called ICL's or implantable contact lenses. However, the ICL's are suspected of initiating cataracts and glaucoma.
As the development of the IOL's became more sophisticated, Ophthalmologists recognized various problems. A typical IOL is composed of an optic, the ‘lens’ part of the structure, and a mounting mechanism called a haptic. The haptics are the part of the IOL that comes in contact with the eye tissue to hold the lens optic in place. There were essentially two major types of haptics which were developed—fiber and plate haptics. Fiber haptics are slender strands of resilient material which are attached at one end to the optic, and which rest, at their other end, against the eye. Fiber haptics have the advantage of being very light and slender. This would seem to make them ideal by causing less damage to the tissue and additionally being aesthetically pleasing because they are very narrow. The slenderness makes it more difficult for someone looking at the patient to see the IOL through the eye. Plate haptics are machined or molded from stock materials and have a central optic and an outer perimeter which rests against the eye. Because of their size, plate haptics tend to be more easily seen from outside in the patient's eye and the addition of extra material weight to the IOL and reduced flexibility as compared to fiber haptics leads to poor fixation and consequent migration or dislocation of the IOL. While, fiber haptics have the disadvantage of initiating a process in which the body builds fibrous tissue or synechiae around the fiber haptic which immobilizes the iris, the larger plate haptic very rarely, if ever, causes such a reaction.
The adverse problems associated with the earlier anterior chamber haptic designs encouraged the development of IOL's for the posterior chamber for the majority of implants.
The surgical process may or may not include removal of the diseased natural lens using a process called phakoemulsification. The more standardized procedure for lens implantation involves removal of a diseased natural lens followed by implantation of an artificial lens. Phakoemulsification of the diseased lens is accomplished through about a 2 to 4 mm (small) incision in the eye and through a capsulorhexis incision in the capsule that encloses the lens in the posterior chamber, then an artificial intraocular lens implant is implanted back through the capsulorhexus into the capsular bag. For other types of procedures, the natural lens may not require removal at all.
As surgical procedures have developed, there is a trend toward reducing the size of the incision in the eye. Although a 3 mm incision does not usually require sutures for healing, it increases the chances of infection, heals slower, and may provide for a slower operation then if an incision of less than 3 mm is used. However, presently IOLs cannot be inserted into a very small incision, as small as 1 mm.